U.N. Secretary-General Antonio Guterres urged an "immediate humanitarian cease-fire" in Gaza, saying that nothing can justify the collective punishment of Palestinians as Israel continues to bombard civilian infrastructure after 100 days.

"We need an immediate humanitarian cease-fire. To ensure sufficient aid gets to where it is needed. To facilitate the release of the hostages. To tamp down the flames of wider war because the longer the conflict in Gaza continues, the greater the risk of escalation and miscalculation," Guterres said at a press briefing in New York.

The war, sparked by a Hamas surprise attack on Israel, has created a humanitarian catastrophe for the 2.4 million people in the besieged strip, the United Nations and aid groups warn, and reduced much of the territory to rubble.

In response, Israel launched a series of indiscriminate attacks that have killed at least 24,100 people in Gaza, mostly women and children, and destroyed hospitals, schools, refugee camps, bakeries and more.

The U.N. says more than three months of fighting have displaced roughly 85% of the territory's population, crowded into shelters and struggling to get food, water, fuel and medical care.

Guterres condemned a humanitarian situation in Gaza that he said was "beyond words."

The "vast majority" of the U.N.'s Palestinian staff have fled their homes and 152 staff members have been killed since Oct. 7, Guterres said – "the largest single loss of life in the history of our organization."

With aid deliveries struggling to get through to a "traumatized people," Gaza now faces "the long shadow of starvation."

"Nothing can justify the collective punishment of the Palestinian people," Guterres said.

The U.N. leader also warned about what he said was an escalating spillover of the conflict, including across the Lebanon-Israeli border. "This risks triggering a broader escalation... and profoundly affecting regional stability," he said.